In the prior U.S. Pat. No. 3,332,327, assigned to applicants' assignee, there is disclosed a pavement marker adapted to be placed on highways and in which the pavement marker front face is inclined at a predetermined angle to the roadway surface so that a self-cleaning effect is provided by virtue of that predetermined angle, whereby that pavement marker achieves initial high optical efficiency and the optical deterioration arising out of dirt accumulation is substantially reduced by allowing the face to be periodically wiped clean by contact with such vehicle tires. In addition, there is disclosed in that patent a cube-corner reflex reflective optical system in which the cube axes of the cube-corner reflective elements are inclined so as to be substantially coincidental with the nominal incoming refracted ray. Pavement markers made in accordance with the U.S. Pat. No. 3,332,327 and similar to the structure disclosed therein and have been extremely successful in operation, and several millions of them have been installed, primarily in areas where no snowplowing of the roads is required. Such pavement marker, while highly effective as a nighttime signal, is substantially ineffective as a daytime marker, because of the nature of its construction, and, in particular, the large metallized area of the reflective portion thereof, which metallizing is required because of the epoxy fill.
As disclosed in the U.S. Pat. No. 3,332,327, mechanical abrasion decreases when the angle of the front face of the lens portion of the pavement marker is increased; however, as that angle increases, the cleaning action obtained by tire wiping on the front face of the lens decreases. The U.S. Pat. No. 3,332,327 further discloses that there is an optimum balance of adequate wiping and limiting of abrasion, and optimum optical effectiveness is achieved, when the angle of the front face of the lens member is disposed at 30.degree. to the horizontal, with a satisfactory result being obtained where such angle is between 15.degree. and 45.degree..
However, when such U.S. Pat. No. 3,332,327 pavement markers are used in areas where, in winter months, abrasive materials such as sand and salt are deliberately distributed over the roadway surface, the abrasion problem becomes particularly acute, as the wiping action of the vehicle tires, combined with those abrasive materials, tends to scratch and grind the front face of the lens and diminish the optical effectiveness or the reflex quality of the pavement marker.
Abrasion-resistant coatings which have not had the hardness of glass have been provided in the prior art for coating the surfaces of a plastic object which might be exposed to abrasive elements. But when used to coat reflective pavement markers, such coatings have either failed to provide the necessary abrasion resistance or have required curing temperatures which were so high that they distorted the plastic material of the reflector, thereby resulting in a serious deterioration of the reflector optics.
A paper entitled "Microsheet Glass Coated Plastics" by W. Hertl was published in February, 1975, at the 30th Anniversary Technical Conference, Reinforced Plastics/ Composites Institute, The Society of the Plastics Industry Inc., Section 9-G, Page 1, a copy of which article is filed herewith. The Hertl article discloses methods of laminating thin glass sheets to thick plastic substrates formed of Lexan and Plexiglas, but teaches nothing about the applicability in pavement markers. The adhesives utilized by Hertl required curing at elevated temperatures for at least several hours. Moreover, in contrast to the present invention, Hertl states that in a single side laminate, the plastic (rather than the glass) is in compression. Also, Hertl does not disclose use of a radiation curable curing system. Finally, applicants conceived use of silane and a glass, adhesive resin and reflector laminate for pavement markers prior to publication of the Hertl article.